Problems hosting a WinForms control in a ToolWindow

Hi,

In my WPF application, I have a WinForms user-control containing Windows Media Player. In addition I have a WPF user-control containing the WinForms media-player control like this:

<UserControl 
   x:Class="MyControls.MediaPlayer"
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
   xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
   xmlns:windowsformscontrols="clr-namespace:MyWindowsForms.Controls;assembly=MyWindowsForms.Controls"
   mc:Ignorable="d" 
   Width="Auto" Height="Auto">

   <Grid Margin="2,2,2,2">
      <WindowsFormsHost>
         <windowsformscontrols:WMPControl x:Name="WindowsMediaPlayer"/>
      </WindowsFormsHost>
   </Grid>
</UserControl>

I'm hosting this media-player control in a ToolWindow like this:

MediaPlayerWindow = new ToolWindow(MyDockSite, "MediaPlayerWindow", "Media Player", null, new MyControls.MediaPlayer());
MediaPlayerWindow.CanRaft = true;
MediaPlayerWindow.CanDockBottom = false;
MediaPlayerWindow.CanDockLeft = false;
MediaPlayerWindow.CanDockRight = false;
MediaPlayerWindow.CanDockTop = false;
MediaPlayerWindow.CanBecomeDocument = false;

My problem is that when the "MyControls.MediaPlayer" is hosted in a ToolWindow, it becomes "invisible". The window just shows a white background. I know that the control is there because I get the Windows Media Player tooltips when moving the mouse over the ToolWindow. The "MyControls.MediaPlayer" control displays normally when hosted in other "normal" windows. I also created a simpler WinForms user-control containing just a button, but got the same behavior.

So my question: Do you know of any problems hosting a "WindowsFormsHost" in a ToolWindow?

Kind regards,

Geir